Scientists at the Oak Ridge National Laboratory (ORNL) have solved the genetic code of bacteria linked to periodontitis. The finding, published in Proceedings of the National Academy of Sciences, profiles the symbiosis region 1 bacteria (SR1), a group of microbes present in many environments, ranging from the mouth to deep within Earth, that have never been cultivated in the laboratory. Human oral SR1 bacteria are elevated in periodontitis. Scientists also found that the SR1 bacteria employ a unique genetic code in which the codon UGA (also called opal, or umber), a sequence of nucleotides guiding protein synthesis, appears not to serve its normal role as a stop code. In fact, scientists found that UGA serves to in­troduce a glycine amino acid instead. “This is like discovering that in a language you know well there is a dialect in which the word stop means go,” said coauthor Mircea Podar, PhD, of the Depart­ment of Energy (DOE) at ORNL’s Biosciences Division. Dieter Söll, PhD, of Yale University, and Dr. Podar led the team that also included scientists from DOE’s Joint Genome Institute who contributed to the analysis of the single-cell sequencing data. The researchers believe the altered genetic code limits the exchange of genes between SR1 and other bacteria be­cause they use a different genetic alphabet. “In the big pool of bacteria, genes can be exchanged between species and can contribute to in­creased antibiotic resistance or better adaptation to living in humans,” Dr. Podar said. “Because SR1 has a change in its genetic alphabet, its genes will not function in other microbes.” This work may provide a path to better un­der­standing the microbiological factors of periodontitis as well as to establishing a frame­work to help scientists interpret genomic data from this bacterium and others that have the same altered genetic code. “So far, no one has been able to isolate and cultivate this type of bacterium,” said Dr. Podar, who noted that there are bugs in our mouth that we have no clue about and, until now, this was one of them. “The genetic information obtained by sequencing one single cell may offer researchers a key to ‘domesticating’ these organisms and studying them in the laboratory.” (Source: ScienceDaily, March 18, 2013)